1. Technical Field of the Invention
This invention relates to developing method and apparatus in photo lithography. More particularly, the invention relates to a technique to recycle developing fluid (developer).
2. Description of the Related Art
In the photo lithography for manufacturing liquid crystal display (LCD) units and semiconductor devices, there are performed sequent processes of: applying photo resist on a substrate to be processed of a substrate (e.g. glass substrate, semiconductor wafer, etc.) at a resist coating process; baking a mask pattern on the photo resist at an exposure process; and allowing photosensitive parts and nonphotosensitive parts defined in the photo resist to dissolve in developing fluid at a developing process. In this way, a resist pattern is formed in the surface of the substrate.
In general, an alkaline solution is used as the developing fluid for the photo resist. In the manufacturing process for LCD disliking alkaline metals and semiconductor devices, particularly, a 2.38% tetramethyl-ammonium hydro-oxide (TMAH) solution as organic alkaline is used widely.
Conventionally, the developing apparatus employs a recycle system for circulating the developing fluid used at the developing process in order to save the consumption of developing fluid per substrate. This recycle system is disclosed in Japanese Unexamined Patent Publication (kokai) Nos. 8-45832 (pages 4–5, FIG. 2), 9-7939 (FIG. 4) and 10-321517 (pages 4–5, FIG. 2). In this kind of developer circulating recycle system, the TMAH concentration is returned to the standard value (2.38%) by either adding new liquid (i.e. 2.38% TMAH solution) to a developing fluid collected from a developing section or adding deionized (pure) water to a concentrate TMAH solution (e.g. 20% TMAH solution). Subsequently, the developing section is supplied with the resulting TMAH solution having the standard concentration (2.38%) as a recycled developing fluid.
In the conventional developer circulating recycle system to restore or maintain the TMAH concentration of the developing fluid to the standard value (2.38%) in the above way, however, there is a problem that if increasing the number of recycling the developing fluid, it becomes difficult to maintain the uniformity in development, especially, linewidth uniformity (CD uniformity). In detail, it is noted that the quantity of resist dissolving into the developing fluid increases with an increase in the number of recycling it. Therefore, even granting that the TMAH concentration is maintained to the standard concentration (2.38%), the weight ratio of solvent (water) in the developing fluid decreases as the quantity of resist or resist content increases. Additionally, it is also noted that a component of resist (resin) has a function to promote development. Combining the former reason with the latter reason, the developing rate is increased, so that the linewidth becomes easy to change into downward trend.